Patent Utility Model No. 62-38032 disclosed a sliding pin of a disk brake, which is applicable to a piston of a disk brake.
In this reference, the sliding pin is cantilevered to one side of the caliper or support, and the piston slides back and forth in a cavity molded in the other side of the caliper, or support. The caliper is moved back and forth in the axial direction of the rotor, and a seal is set around the perimeter of the cavity to form an airtight lock with the circumference of the piston. To seal off the sliding surface of the piston and cylinder cavity, a peripheral groove, into which a boot is set, is provided around the circumference of the piston from the rim of the sliding cavity, and depressed channel, with a passage into the peripheral groove, and extends towards the free end of the piston to a length virtually equal to the width of the peripheral groove and slightly longer than the dimension of the seal in the axial direction.
A disk brake device as described above has the following problems:
1. The sliding pin is inserted into a pouch-shaped caliper boss which is closed on the rear end while the open end is sealed tightly by a seal; hence air inside the caliper boss remains compressed until the sliding pin is inserted to a point where the depression passes through the seal, making it difficult to install the sliding pin. PA1 2. Moreover, since the depression penetrates through the seal in order to exhaust the compressed air, the seal is damaged by the edge of the depression, which markedly reduces the tightness of the seal and detracted from the seal's useful life. PA1 3. Normally, the expandable end of the boot is elastically affixed to the peripheral groove around the guide pin with an interference fit; therefore the width (the dimension in the axial direction) of the expandable end of the boot is set to be wider than the width of the guide pin groove. Moreover, since the width of the peripheral groove is set to be equal to the axial length of the depression, then the width of the expandable end of the boot becomes longer than the axial length of the depression. This means that the expandable end of the boot covers the depression, making it difficult for air inside the boot to be exhausted externally, thereby canceling the purpose of the depression. PA1 1. A boot is installed in a caliper; PA1 2. Compressed air is introduced into the cylinder while a piston is pressed against a boot; PA1 3. A boot is expanded to be elastically affixed to the circumference of the piston; PA1 4. The piston is then inserted into the cylinder cavity of the caliper; and then PA1 5. The boot is affixed to a boot groove of the piston. PA1 1. In the second step, compressed air is shut in the piston, boot, and piston seal, thereby causing excessive expansion of the boot. PA1 2. This excessive expansion of the boot causes the boot be put out of joint from the piston. PA1 3. To prevent the above disconnection, a stick may be inserted between the piston and the boot to exhaust the compressed air. PA1 1. In assembling the disk brake device, compressed air introduced from the fluid inlet and accumulated in the dust boot can be exhausted via an air vent groove provided around the circumference of the piston. This configuration makes it extremely easy to assemble the device. PA1 2. The axial length of the dust boot leg is shorter than the axial length of the air vent groove, in which case, the leg does not cover the air vent groove, and the compressed air within the dust boot can be adequately exhausted via the cover. Again this configuration makes it extremely easy to assemble the device. PA1 3. The length from the bottom face of the cylinder cavity to the front end of the seal groove is shorter than the length from the bottom face of the piston to the back end of the air vent groove. Hence during assembly, even if the piston were to be pushed down to the bottom face of the cylinder cavity, the air vent groove will not catch on the seal. This prevents any damage to the seal, making it more durable.
A second type of conventional disk brake has a rotating disk rotating in tandem with a wheel. A pair of friction pads sandwiching and pressing against the rotating disk are provided to create friction. A caliper straddles a portion of a circumference of the rotating disk. One or more pistons are housed to slide within a cylinder cavity bored in the caliper and push the friction pads against the rotating disk. A seal fitted into a ring-shaped groove provided around an inner face of the cylinder cavity is designed to maintain a fluid-tight seal with the piston. A dust boot is installed between an open end of the cylinder cavity and a ring-shaped boot groove molded on a circumference of the piston to seal off the sliding surface.
The assembling process of this piston is a follows:
The following problems are presented in the assembling process described above: